Regularly taking aspirin and ibuprofen may help protect against some forms of skin cancer, research suggests.
An Australian analysis of all studies to date found that non-steroidal anti-inflammatory drugs (NSAIDs) reduced the risk of squamous cell carcinoma by 18%.
The drugs have previously been linked to a reduced risk of other cancers, including colon cancer.
Experts said staying out of the sun and wearing sun cream were the most effective ways to avoid skin cancer.
The theory that NSAIDs such as aspirin may protect against skin cancer has been raised before, but the overall evidence had been unclear.
So researchers did an analysis of nine studies looking at use of the drugs and the risk of squamous cell carcinoma - the most common form of skin cancer.
Reporting in the Journal of Investigative Dermatology, they found that taking any NSAID was associated with an 18% lower risk of developing the cancer.
And taking NSAIDs other than aspirin was linked with a 15% reduced risk.
It is the most convincing evidence so far that the drugs help prevent the development of squamous cell carcinoma.
But experts still cannot be sure of the effects because some factors - such as how much sun someone is exposed to or even what doses of the drugs they take - have been difficult to pin down with any accuracy.
It is thought that NSAIDs, which also include diclofenac, may prevent skin cancer because they inhibit an enzyme called COX-2, which is involved in tumour development.
The researchers did find a greater degree of reduced risk associated with use of the drugs in people with pre-cancerous growths or a history of skin cancer.
It raises the possibility that the drugs could be used as a preventive treatment in some groups.
Some people are prescribed NSAIDs long term for conditions such as arthritis, but they are not recommended for regular use in healthy people because of side effects, which can include, in rare cases, bleeding in the stomach.
Prof Dorothy Bennett, an expert in cell biology, at St George's, University of London, said the results were worth knowing about.
But the drugs' side effects would likely prevent their routine use in everyone.
"Noting that most [squamous cell carcinomas] are curable by surgery if caught early, this reduction in risk is interesting, but it is hard to say whether it is worth taking action over it."
Prof Brian Diffey, emeritus professor of photobiology, dermatological sciences at Newcastle University, said that reducing the risk of skin cancer by the same magnitude seen in the study could be done with a small reduction in sun exposure.
"Given that long-term therapy with NSAIDs is not without risk, a safer option for those who wish to reduce their likelihood of skin cancer may be to spend a few minutes a day less outside."